But we donât owe our e_xpanding bustlines to modern fitting techniques alone.

Back in the Fifties, the _average woman wore a B-cup â a full size smaller than todayâs larger size. Itâs clear that our dimensions have shifted, but why?
Generous proportions: Terri Smith has L-cup breasts

Generous proportions: For women such as Terri Smith, 21, the new L-cup could provide welcome relief

Fat is the first answer most experts will give. Professor Michael Baum, an expert in breast cancer, says: âFat is laid down on breasts as much as thighs or bottoms. We are experiencing an obesity _epidemic, so the increase in womenâs measurements isnât that surprising.â

But this is only part of the story. After all, women such as Terri do not appear to be _carrying much excess fat _elsewhere on their bodies. As Terri says: âThe rest of my body is quite slim. Yet throughout my teens my boobs went up a couple of cup sizes every year.â

Anna Prince, from Bravissimo, agrees: âThere is a total misconception that itâs _unusual to be big-boobed and small-bodied. Weâve been _contacted by more than two million women since we started in 1995, the vast majority of whom are small in the body and big in the bust.â

So, whatâs going on? Why are the nationâs breasts getting bigger?

Dr Marilyn Glenville, a nutritionist _specialising in womenâs health and hormones, says: âItâs clear that weâre not just talking about fat, but increased levels of breast _tissue, too.

âSo we have to look at what stimulates breast tissue growth â and thatâs oestrogen, the female sex hormone. _Oestrogen is what changes our body shape during puberty.â

The link between increased oestrogen levels and bigger breasts is so clear that there are even âbreast-enhancingâ _supplements on the market â such as Perfect C Breast Enhancer capsules â containing ingredients such as fennel seed and fenugreek, which are said to have oestrogenic properties.

Dr Glenville says: âIt makes sense to look at the ways in which our exposure to all types of oestrogen â the hormone our own bodies produce and oestrogenic chemicals we come into contact with â has changed over the years.â

âGirls today reach puberty earlier than ever before, and are going on to have fewer _children and breastfeeding for less time. As a result, we have far more periods than our ancestors would have had and we are exposed to more monthly surges of oestrogen, which stimulates ovulation.â

In addition, todayâs young women were born to the first _generation of women on the contraceptive Pill. Early versions of the Pill contained far higher dosages of synthetic _oestrogen than they do today, and little is known about the long-term impact of this increased hormone exposure on future generations.

So, could the _changing shape of our breasts indicate an increased sensitivity to oestrogen?

Dr Glenville says: âPregnancy and breastfeeding have a _protective effect against breast cancer because they control the hormones which stimulate the growth of new cells in breasts.

âBut with more women today putting off pregnancy until later in life and having fewer children, they experience many more monthly cycles than previous generations did, and are exposed to more oestrogen.

'Girls today reach puberty earlier than ever and are going on to have fewer _children. As a result, we have more periods so we are exposed to more surges of oestrogen'

âIâm certain that if you looked at photographs of Victorian women, who on average had five or six children, youâd find them comparatively flat-chested.â

But, of course, that is far from the only difference between womenâs lives then and now.

HRT also tops up depleting oestrogen levels in menopausal women, who â like women on the Pill â often go up a cup-size or two when they begin a course of treatment.

But itâs not just women on the Pill or HRT whose _oestrogen levels, and cup-size, might have increased as a result.

In 2002, research published by the Environment Agency showed that an âexquisitely potentâ form of oestrogen â which is believed to have entered the rivers through the urine of Pill and HRT-users â was responsible for changing the sex of half of all the male fish in British lowland rivers, and could be contaminating the water supply.

Now, it has been suggested that the influence of these xenoestrogens (literally âforeign _oestrogensâ) could be responsible for the rapid decline in male sperm count and fertility.

âWe canât assume these _pollutants have no effect on us,â says Dr Glenville. âThere are many questions still to be answered, but if xenoestrogens are potentially responsible for declining male fertility, they are potentially affecting women, too â and the proof could be in our bras.â

So how do we avoid these surplus hormones? The answer is, we canât. And it may come as a surprise to know that they are found in everyday items.